Project Summary Evolutionary medicine leverages the power of naturally occurring phenotypic differences derived through adaptation to investigate genetic mechanisms underlying diseases, including neurological and metabolic disorders. The Mexican cavefish exhibits a dramatic evolution of sleep loss compared to ancestral surface fish of the same species, providing a unique and powerful model to identify genetic factors regulating sleep. The proposed experiments will implement genetic technology in Mexican cavefish to determine the contributions of Orexin, a highly conserved wake-promoting neuropeptide, to evolutionary-derived sleep loss. This proposal will also develop a detailed neuroanatomical brain atlas of diverse neuronal cell types and establish a genetic system for whole-brain calcium imaging in freely moving animals. The generation of the brain atlases in conjunction with whole brain calcium imaging will be used to define neural signatures of sleep and wakefulness. These experiments will provide critical insight into the mechanistic basis of sleep regulation. The transgenic tools and techniques established in this study will provide a valuable resource that can be applied to address questions beyond the scope of this proposal, including diseases such as eye-degeneration, obesity, hyperphagia and aggression commonly studied in cavefish.